Arfa Daily spake thus:

wrote in message
ups.com...

I need to design a circuit that I can tell it to start (digitally),
and then it will tell me when 10 minutes have passed. I just need
to be pointed in the right direction. What's the difference bewteen
a timer/clock/counter. I have a good understanding of circuit
theory but does anyone know of a good IC that can be surface
mounted (and is cheap) that I shoulod use. Any help or tips are
greatly appreciated

All depends on how accurate that you need to be really. A simple
timer circuit - the CMOS version of the good old 555 is quite capable
of this sort of delay - could be set up fairly precisely in
monostable mode, to do 10 minutes or thereabouts, say give or take a
few seconds.

If you really need an accurate 10 minutes, then you need to use a
counter. You would start with a clock generator, probably a standard
watch crystal at 32.768kHz, then divide it down to get your 10
minute interval. If you don't want to divide as far, you can start
with a lower frequency, but it's usually convenient to use a ' binary
' frequency. A 16 bit counter on the end of a 32k clock, will get you
down to a second. You then need a further 10 bits of counter and a
bit of AND-ing to get you to the 10 minutes.

Since it looks like 32.768 kHz is the lowest-frequency oscillator
available (checked both Digikey & Jameco), I'd say all you need would be
one of them (a complete oscillator, not a crystal) and 2 counter chips
(like the 74HCT4040), one set to divide/16 as you explained, the other
/10. This would give you a TTL pulse at the end of the countdown cycle.


--
The only reason corrupt Republicans rule the roost in Washington
is because the corrupt Democrats can't muster any viable opposition.